If you choose to play craps at an online casino, obviously you won't be rolling any physical dice, instead you'll be at the mercy of a “random number generator” (RNG). The random number generator in an online casino is what determines the outcome of every game, craps certainly included. While in practice these RNGs are typically safe and fair, it's certainly a good idea to have a rudimentary understanding of how they work.

When you use a RNG it's not just simply a matter of the computer “picking a number.” A computer can't do anything without a set of instructions. The problem is that selecting a number “at random” is not like adding two numbers together. There is no deterministic right answer, and therefore the computer, with all its mathematical powers, simply can't select a number at random. At least it can't without a little assistance. 

So, what the computer could do is progress through a set of numbers. Let's say we're trying to roll one die. We roll it the first time and the computer outputs a 1, the second time a 2, and so on. When we roll the die for a seventh time, the sequence has started over and we get a 1 again. While the die rolls here will certainly be evenly distributed, they are very far from random!

In our example above we have one die with six possible outcomes. If we add a second die the number of possible outcomes grows to 36 (6x6). So now, let's assign each of these 36 outcomes a number 1 through 36 in a very basic computer program. All this program does is take our input value (again 1-36) and give us an output which will be the number on the first die, and the number on the second die.

Now let's imagine we had a 36 sided die in front of us (bear with me, I'm coming to a point) if we rolled that die while sitting in front of our computer we could see the result of that die, say 7. We could then type “7” into the simple computer program and out would come results for our two die. In this way we could obtain an evenly distributed and random set of results, but note that all of the randomness is introduced from outside the system.

This is essentially how a true random number generator works. It takes the “seed” from an external source runs it through an equation, and then outputs a result from a table of possible outcomes. Not all seeds are created equal, however. Not too long ago, online poker sites were using mouse movements and the time on the system clock to help generate their seeds. While these seeds were reasonably secure, they're far inferior to the RNGs most sites use today.

The input that creates the seed in a true random number generator can get down right exotic. Some of the inputs used are atmospheric noise (as detected by a standard radio),  radioactive decay, and even snapshots of lava lamps. As strange as it is, to think that weather patterns could be affecting your casino results, it's absolutely true. The common thread between these seed generators is that they are something out in the real world that has legitimately random behavior. To recap, you can't get a random number out of a deterministic system, you can only get a random number from something... well, random!